CHARACTERIZATION OF K<SUB>V</SUB>7.2/7.3, K<SUB>V</SUB>7.2/7.5, AND K<SUB>V</SUB>7.3/7.5 CHANNEL PROPERTIES: ROLES OF SUBUNIT COMPOSITION AND PHARMACOLOGICAL MODULATION

The K_v7 channel family consists of 5 different subtypes and is encoded by the KCNQ1- 5 genes. K_v7.2, 7.3, and 7.5 are the basis for the so-called M-current and are predominantly expressed in skeletal muscle and the brain, where they stabilize the resting membrane potential, contribute to neuronal afterhyperpolarization, regulate the firing frequency of tonically active neurons, and support neuroplasticity by maintaining theta resonance. To enable the characterization of distinct K_v7 heteromers, we designed three vectors containing either the KCNQ2-P2A-KCNQ3, KCNQ2-P2A-KCNQ5, or KCNQ3-P2A-KCNQ5 sequence. An additional GFP tag at the end of the vector was used to visualize transfected cells, which were analyzed using whole-cell patch clamp recordings. Obtained currents were evaluated for current density (CD) evoked at a test potential of +40 mV, potential of half maximal activation (V_h), and their activation kinetics. We found significantly larger CD and more hyperpolarized V_h when compared between Kv7.2/7.3 (CD= 448.22 pA/pF, V_h= -45 mV) and K_v7.2/7.5 (CD= 83.16 pA/pF, V_h= -41 mV) heteromers. Furthermore, V_h of K_v7.2/7.3 was more depolarized compared to K_v7.3/7.5 (-57 mV) heteromers. Finally, there was a significant difference in V_h of 16 mV between K_v7.2/7.5 and K_v7.3/7.5 heteromers with the latter being more hyperpolarized. Overall activation kinetics of K_v7.2/7.5 are significantly slower at depolarizing test potentials > -20 mV compared to K_v7.2/7.3. Thus, the different subunit compositions appear to be distinguishable based on their activation kinetics, current density and V_h. Further experiments will focus on the effect of neurosteroids on different K_v7 subunit compositions.